The antenna effect is a form of plasma-induced gate dielectric (e.g., silicon oxide) damage that can cause yield and reliability problems during the manufacturing of MOS integrated circuits (ICs). Semiconductor fabs generally have a set of antenna rules for avoiding this problem.
An antenna violation is caused by the accumulation of excess electrical charge. A typical completed integrated circuit (IC) has “nets” including at least one driver which includes a source diffusion or drain diffusion, and at least one receiver including a gate electrode (e.g., doped polysilicon) over a thin gate dielectric that is over the substrate. Since the gate dielectric may be quite thin, such as only being a few molecules thick, a concern is the dielectric breakdown of this dielectric layer. Dielectric breakdown can happen due to the resulting electric field across the dielectric if the net acquires a voltage higher than the normal operating voltage of the IC.
Once the chip has completed fabrication, the antenna effect generally cannot happen, since every net has at least a source and a drain connected to it which protects it. The source and drain form a diode, which conducts in the forward direction or breaks down at a lower voltage than that of the gate dielectric oxide (either forward diode conduction, or reverse breakdown), and either conducts or breaks down non-destructively. This action protects the gate dielectric from dielectric breakdown.
However, during fabrication of the IC, the gate dielectric may not be protected by any diode, such as while metal 1 is being etched. Since metal 2 is not formed yet, there is no diode connected to the gate dielectric. Accordingly, if electrical charge is added in any way (such as by plasma etching) to an isolated piece of metal 1 it can rise to reach a voltage level capable of breaking down the gate dielectric. In particular, plasma etching or reactive-ion etching (RIE) of the first metal layer can result in this situation, where the net is disconnected from the initial global (blanket) metal layer, and this etching adds charges to each isolated piece of metal 1.
Leaky gate dielectrics, although a problem for power dissipation, help avoid dielectric damage from the antenna effect. A leaky gate dielectric can prevent a charge from building up to the point of causing gate dielectric breakdown. This leads to the result where a very thin gate dielectric may be less likely to be damaged than a thicker gate dielectric because as the gate dielectric grows thinner, the leakage goes up generally exponentially, but the breakdown voltage shrinks only basically linearly.